Most manufacturers of seat suspensions have sold, or are currently selling, a conventional bell crank mechanical suspension system. The main components of this type of seat suspension typically include:                Two support brackets welded to the top plate (e.g. the seat platform);        Two extension springs;        A welded bell crank sub-assembly that includes two bell crank arms, a bearing tube between the two bell crank arms, and a spring mounting shaft fixed to the bell crank arms;        A spring hanger bracket;        A tension adjust shaft;        A knob attached to the tension adjust shaft;        Two flanged bearings inserted into the tube;        A pin attaching the bell crank assembly to support brackets and e-rings at both ends; and        A roller attached to the bell crank assembly with a pin and e-rings at each ends.        
The above components are generally assembled at the same time as a complete seat suspension. Thus, the above components are also assembled at the same place as the rest of the seat suspension.
The invention and background for the invention relates to seat suspensions disclosed in commonly owned U.S. Pat. No. 5,794,911, which issued in August of 1998, and U.S. Pat. No. 5,927,679, which issued July of 1999, wherein a suspension height or vertical adjust mechanism acts independent from that of the suspension weight adjustment or energy mechanism.
Traditional means for providing such height and weight adjustment functionality is that of loose members being systematically fixed to a partially assembled seat suspension, comprised of a top and bottom plate and connected linkage capable of lifting the top plate in a vertical fashion with respect to the bottom plate. This means of assembly limits the design of the energy and vertical adjust components to that of elements that can be installed and assembled as loose members to the seat suspension in the restricted space available between the seat platform and base. Thus, no prevailing interference points can exist within the suspension between the platform and base as the vertical adjust and energy adjustment components are systematically assembled to the suspension. This constraint may require additional space within the suspension envelope. This can result in, for example, taller collapsed height or wider linkage between plates than necessary. It may also require specialized tools for assembly. The traditional embodiment may require additional components that provide unnecessary redundancy at increased cost to attach the vertical adjust and energy adjust components.
One typical approach of providing height adjust in a conventional bell crank suspension is an adjustable up-stop. A mechanical device is adjusted to provide two or more positions that each provides a different limit for the upward travel of the suspension linkage. In order for an operator or seat occupant to change their static vertical position they also need to either increase or decrease the spring tension adjustment, which typically requires a significant expenditure of work or energy. Moving the up-stop has no effect on the operator's vertical position because the up-stop adjustment does not decrease or increase the preload of the springs. Without changing the spring preload with the weight adjustment control, the operator will return to the same static vertical position regardless of the up-stop setting. Thus, two adjustments disadvantageously must be made to change the operator's vertical position.
Damping in compact suspensions is typically achieved by connecting the damper between the upper and lower housings, e.g., connecting the damper between the base and platform. This arrangement produces nonlinear damping characteristics. The effective damping force acting to isolate the operator significantly decreases as the suspension collapses. This is an undesirable behavior for effective vibration isolation.
Another shortcoming of conventional compact bell crank suspensions is compromised vibration isolation. The compact size limits the optimization of the bell crank leverage ratio, which results in higher spring rates, higher joint loads, and therefore more system friction.
What is needed is a seat suspension that overcomes one or more of these deficiencies. What is also needed is a seat suspension that better facilitates assembly and installation. What is further needed is a seat suspension of simple design that has a minimum of components so as to simplify assembly and installation while reducing cost. What is still further needed is a seat suspension of compact construction that results in a shorter collapse height.